SOPHIA NON-WORKING SPEEDOMETER

My speedometer is crazy, it wobbles up and down and sometimes it actually does work right, but it is intermittently. My tripometer and odometer are part time workers as well. I have just replaced my speed sensor; prior to replacing this the speedometer was constantly at " 0" and after the replacement, it jumps around. What is the problem? Is the speed sensor not working right or is there something else that I should be doing to fix the problem.